Paper and Its Uses

Front matter

Paper and its Uses

A TREATISE FOR PRINTERS

STATIONERS AND OTHERS

Raw Materials

PAPER AND ITS USES

CHAPTER I

RAW MATERIALS

Papermaking is an industry which is in many ways handmaiden to other industries. In the case of letterpress, lithographic, and plate printing it furnishes the supporting medium, without which the dissemination of knowledge would be more difficult. Long ago the printer appreciated the fact that the invention of the art of typography enlarged the sum of the world's knowledge, but perhaps he has not always been ready to give the papermaker a fair share of the credit. It must be conceded that while many things will serve as printing surfaces, the question of cost decides against their general use, and that paper is the principal material employed for written and printed books. It is with these uses that this work deals, while some others are touched upon.

The history of papermaking takes us back beyond the Christian era—the Chinese being credited with the production of paper from vegetable fibres about 80 to 150 B.C. The ancient Egyptians made paper from the stems of the tall reed which we know as the papyrus. By skilfully flattening out layers of the stems, forming them into sheets, and preparing the surface for writing, the Egyptians provided themselves with excellent paper.

European papermaking dates from the eleventh century, and English papermaking from the fifteenth century. The colophon to Wynkyn de Worde's "De Proprietatibus Rerum" mentions the paper mill of John Tate at Stevenage in Bedfordshire. Early English papers were made from rag fibres, and rag papers still hold the premier place.

Cellulose is the substance of which the permanent cell membranes of plants are composed, and it forms the bulk of the tissues of wood and similar plant structures. In most cases the presence of colouring matter and various waxy and resinous substances taken up by the growing plant render the cellulose very impure, and it is desirable that, as far as possible, all impurities should be removed before the fibres are made into paper. Cotton is the purest form of cellulose found in nature, 91 per cent. of the natural cotton fibre being pure cellulose, while esparto yields only about 50 per cent. of its weight as cellulose. Notwithstanding the many different varieties of plants, the chemical composition of the fibres is practically identical. One of the principal characteristics of cellulose is its extreme permanence, which is principally due to the fact that it forms but few chemical combinations with other substances.

Vegetable fibres of all kinds may be converted into paper, but no new fibre threatens those now employed, unless it can be obtained in large quantities, responds readily to the usual bleaching reagents, and can be delivered to the papermaker at a price which enables it to compete successfully with the fibres at present in use at the paper mill. In some cases the plant fibres are reduced to pulp near the place of growth, in others the raw material is transported in its entirety. Other sources of supply are the wastes of other industries, and wastes which have no other uses.

The classification may take place as follows: (a) waste—rags, sails, sacking, ropes, textile wastes, waste paper; (b) plant stems and wood—straw, esparto, bamboo, papyrus, hedychium; (c) pulps or half-stuffs—straw, esparto, delta cellulose (or reed pulp), bamboo, chemical wood, mechanical wood.

Rags are the cast-off fabrics of the civilised world. Having served their purpose in administering to the comfort of mankind, they are sorted, graded, and offered in the market for papermakers. For the manufacture of paper for bank-notes new linen cuttings are used, but this is an exceptional material for a special purpose. Sail cloth, bagging, sacking and ropes, made from hemp, jute, manilla hemp, having reached the waste market, are regenerated in the mill as paper. Waste paper of all kinds is sorted and re-made into paper or boards.

Esparto is the principal material that finds its way to the papermaker in its original state. It is a wiry grass, growing extensively in Spain and Africa, and is harvested and packed in bales for export. Straw is generally imported as half-stuff. Bamboo, papyrus, and hedychium are being used in quite a small way in this country, but may be extensively used in the future.

Straw, esparto, reed pulp, and bamboo are obtainable as half-stuff or pulp, that is, they are already divested of the portions of the plant which are non-fibrous, and therefore useless to the papermaker. Wood pulp is the chief material converted into paper, and may be prepared as chemical or mechanical. Chemical wood pulp is prepared, after removing the bark from the felled trees, and cutting the logs into chips, by boiling with caustic soda solution (soda pulp), with a mixture of caustic soda and sulphate of soda (sulphate pulp), or with bi-sulphite of lime (sulphite pulp). Mechanical wood pulp is obtained by cutting the logs into short lengths, removing the bark, and grinding to pulp on a large grindstone, the surface of which is freely supplied with water. The water renders the reduction to pulp an easier matter, and also serves to carry the pulp forward for subsequent treatment.

In speaking of paper it is usual to refer to the material from which it is made, e.g., rag, rope, esparto, manilla or wood papers. It does not always follow that the papers are composed entirely of those fibres, but the prefix of "pure" or "all" will generally indicate the genuine articles. Paper which is free from mechanical wood pulp is sometimes referred to as "free."

The strongest and best papers are made from cotton or linen rag fibres. Linen is made from the fibres of the flax. In the raw state the fibres are from 1 inch to 1 inches in length, and less than of an inch in diameter. Examined microscopically the fibres appear to be smooth, cylindrical, with markings like the joints of a cane, slight cross markings, and a very fine channel running through the fibres. Papers made from linen are close, strong, and durable. Cotton is the seed-hair of the cotton plant, having a length of 1 to 1 inches with the diameter about the same as that of linen fibres. Cotton is tubular, has a large channel, and on drying the tube collapses and twists upon itself, as many as 300 twists in the length of a single fibre having been observed. This twisting assists in keeping the spun cotton together, and also makes the felting of the subsequent paper more efficient. Papers made from cotton are softer than those made from linen, and the tenderest rags, such as worn muslins, are employed for blotting papers. Hemp is obtained from the stem of the hemp plant, and the papermaker receives it in the form of old ropes and string. The dimensions and properties of the fibre are similar to those of the fibre of linen. Jute is the inner bark of an Indian plant, producing fibres of an inch in length by of an inch in diameter. The fibre is smooth, difficult to bleach, but the resulting paper is strong and tough. The fibre of the manilla hemp is not as long as the ordinary hemp, being about of an inch by of an inch, cannot be bleached to a good white, so a white manilla paper is considerably lower in colour than other white papers. Manilla paper is, however, very tough and strong, and though a large quantity of "manilla" paper is made entirely of wood pulp, there is a great difference between the real and the imitation.

The fibres from straw are small, only about of an inch by of an inch, and consequently straw papers are much weaker than those made from longer and broader fibres, but, as an admixture, straw still finds a place in writing papers, giving translucency and rattle. Esparto fibres are also very short and fine, about to of an inch by of an inch, making a light bulky paper when used by itself, and blended with other materials—with rags for good writings, and with chemical wood for fine printings and litho. papers—to impart special characteristics, such as opacity and softness, which may be lacking in the other fibres. The well-known featherweight papers, used for bulky volumes of fiction, are frequently manufactured from esparto fibre alone.

The fibres of the various wood pulps vary considerably in length, breadth, and thickness, being from of an inch to of an inch long, and generally very thin. Fibres of various shapes are met with in wood pulps, some not unlike linen fibres, but many others so distinct as to be unlike all those that have been already described. Broad, ribbon-like fibres, some pitted, and others perforated, all are very thin, lying closely together, so that a paper made entirely from sulphite wood pulp is rather harsh and fairly transparent. Papers produced from soda pulp are softer and more opaque than those made from sulphite pulp. Mechanical wood pulp is made up of little pieces of wood with all the resins and other impurities of the original wood, and when examined carefully, the fragments of wood can be seen, and the splinters appear to be held together by the plant cells. Mechanical wood pulp possesses very little felting quality, and requires the addition of larger fibres, such as chemical wood, in order to make paper successfully.

From the foregoing list and descriptions it can be seen that papermakers have a variety of fibres at their command, and it is by selecting, sometimes by blending, fibres of different characteristics, that the manufacture of the large variety of papers is possible. Some of the demands made by the world of paper users are for papers which are very strong or very soft, absorbent, resistant to grease or water, very light, very dense, and the selection of the fibres and their treatment call for special knowledge and skill on the part of the papermaker.

In addition to fibre, most papers contain sizing, sometimes loading or filling. Sizing may be animal or vegetable, the animal size being gelatine or glue obtained from various animal substances, and the vegetable size being made of a combination of resin with soda. Alum is used to assist in fixing the size in the paper. Mineral matters are employed for filling or loading; china clay is the principal, others being barium sulphate (barytes, blanc fixe), calcium sulphate (gypsum, terra alba, annaline, pearl hardening, crown filler), satin white, magnesium silicate (asbestine, talc, agalite). Colouring matters are required for the majority of papers. For white papers small quantities of blue and red colours are used, while for coloured papers aniline dyes are employed in a large variety, as well as the various pigments.

Reduction to Pulp

CHAPTER II

REDUCTION TO PULP

Whatever material may be used for making into paper it has to undergo stages of preparation which can be divided into removing all foreign matter and dirt, reduction to fibrous state, bleaching, beating, and lastly converting what is the pulp into paper. If the material has already been manufactured, as in the case of rags, ropes, sails, sacking, and other textiles, the first process is somewhat simpler than in the case of really raw materials, such as esparto, bamboo, or wood. But here again the first and second operations may have been carried out before the papermaker handles the material, for wood, esparto, and bamboo are imported as pulp boards. In the case of esparto the quantity so imported is very small, but the quantity of wood pulp is enormous. It will be advisable to take the materials in order, so that the difference as well as the similarity of treatment may be traced.

Rags are purchased already graded. There are some twenty to thirty grades of rags regularly quoted in the market reports, and the layman might fancy that the papermaker could unpack the bales and proceed to make paper from these graded rags. Unfortunately he finds a large quantity of undesirable material, such as silk, wool, buttons, elastic, and dirt, that must be removed. First the rags are sorted, and cut into pieces of uniform size, the undesirable parts mentioned being put aside as useless, and the seams cut open or thrown out. Standing at a bench, the top of which is wire netting, the sorter takes rags from a pile, and cuts them on a scythe-like knife which stands out obliquely from the bench. A large amount of dust escapes through the netting, and the rags are sorted into bins as more suitable for one class of paper than another. The rags are next taken to the willow or dusting machine, where they are subjected to violent treatment, the teeth of the machine carrying the rags against other teeth, giving them a thorough shaking and loosening the dust, which falls away. As they are cleaned, the rags are taken to the top of the building by a travelling band and dropped into the mouth of a boiler prepared to receive them. For rags a special spherical rotary boiler is employed, and when a charge has been filled in, a definite quantity of a solution of caustic soda in water is added. The lid is securely fastened, steam is passed in, and the boiler is kept rotating slowly for about eight hours. When the dirt in the rags has been thoroughly loosened the rotation is stopped, steam is shut off, the dirty water is run off, clean water is run in. The boiler is again revolved, the rags rinsed, and then the lid is removed and the boiler emptied by continuing the revolution.

Next comes the washing and breaking, both of which may be carried out in the beating engine. The beating engine, of the Hollander type, consists of a large vessel with rounded ends, with a central division running down the length of the engine. Two cylinders revolve: one, a very heavy cylinder known as the beating roll, reaches to the bottom of the engine and bears a number of knives on its surface, which knives, in conjunction with a bedplate also bearing knives, break the rags into smaller fragments and open the threads, loosening the fibres, and allowing dirt to come away. The second and smaller cylinder is employed as a washing drum. It is covered with wire gauze, through which the water passes, and as the drum revolves the dirty water passes into the interior, where a number of bucket compartments carry the water and pass it through the axis of the drum to the waste pipe. When the rags are filled into the beating engine clean water is run in, the beating roll is kept out of contact

with the bottom knives, and the rags are kept in circulation. The washing cylinder is in action, and the roll being gradually lowered the dirt is eliminated. When this stage is reached the washing drum is lifted, the beating roll lowered, and the rags are gradually reduced in size until they attain a state of fibrous pulp, being known technically as "half-stuff." In most instances the next process is bleaching. There are special drawing papers, of which "O.W." and "Unbleached Arnold" are examples, which are the colour of the original rags, no bleaching having taken place. But usually a weak solution of bleaching powder (chloride of lime) is let into the engine and thoroughly mixed with the pulp. When the bleach is thoroughly incorporated the half-stuff is let down into large tanks, made of stoneware or cement, having perforated bottoms, and there the bleach completes its task, and the pulp is allowed to drain.

Next comes the beating, at which stage the blending of different fibres may take place. The object of beating is to reduce the bleached pulp to fibres, and to reduce the length of the fibre in accordance with the requirements of the paper to be made. The rags are chosen according to the class of paper desired—softer rags for soft papers, and, of course, stronger rags for strong papers. For blottings, filter papers, and lithographic papers, soft rags, sharp beater knives, quick beating are adopted. For dense, hard papers, such as ledger, type-writing, bank, imitation parchment papers, duller knives, slow beating, with a gradual lowering of the beater roll is the order. The normal time for beating the pulp for an ordinary rag paper may be taken as eight hours.

To take the next material, esparto, and to follow it in the same way. Esparto arrives in bales, fastened either with ropes of esparto or with iron bands. Esparto travels through the mill in the same way as rags, that is, from the ground floor, where it is unpacked and dusted, upwards by means of a series of claws, along a travelling band where pickers remove foreign substances. In its travel broken fibres and dirt escape, and the grass arrives at the mouth of an upright cylindrical boiler, stationary, and so arranged that the boiling liquor is vomited over the mass of esparto. The boiler is filled, and a fairly strong solution of caustic soda is run in, the manhole is fastened down, and steam under pressure introduced. After several hours boiling the siliceous and waxy substances taken up by the growing plant are dissolved, the dirty water is run out, small quantities of clean water let in to wash out as much soda as possible. Most of the soda is recovered, but that process, though of great importance to the paper-maker, need not be treated here. The washed esparto is conveyed to the breaking engine for treatment similar

to that given to rags, being washed, broken, and bleached. In many mills the half-stuff is carried over strainers, and by the use of the presse-pate machine (a paper-making machine with only a "wet end") made into sheets. The half-stuff in sheets is filled into trucks and stored or taken direct to the beaters. Owing to the small dimensions of esparto the reduction to the fibrous state is easily accomplished, and very little beating is necessary.

Wood, chemical or mechanical, usually finds its way to the paper mills in the form of pulp boards, and is known as chemical or mechanical wood pulp. No boiling is necessary, but the boards are fed into the breaking engine, and reduced to half-stuff, a little bleach liquor added to chemical wood, and the contents of the engine, when sufficiently reduced, are let down to the draining tanks for the bleach to expend itself. Then the pulp is ready for the beating engine, where it is reduced to the necessary degree of fineness.

Some materials are more effectively reduced to pulp in the edge runner or kollergang. This machine is similar in appearance to a mortar mill, but the arrangement is slightly different. The pan of the machine is stationary, and the stones revolve and travel round the pan. Only a small quantity of water is used with the pulp, and waste papers which require rubbing apart only, and strong wood pulps of which the fibres are drawn out, and not in any way reduced in length, are treated in this machine more economically and more effectively than in the beating engine.

Manufacture of Hand-made and Mould-made Papers

CHAPTER III

MANUFACTURE OF HAND-MADE AND MOULD-MADE PAPERS

English hand-made paper is still looked upon as the best paper obtainable. Some fourteen firms still make paper by hand, and although the number does not increase, there is no sign of its diminution. The reduction of the rags to fibre was treated in the last chapter. Before leaving the beating engine the colouring matter is added; in the case of a white paper a small amount of blue is necessary to counteract the grey appearance which the natural pulp usually assumes. This is merely equivalent to the blueing which is resorted to for giving linen a bright appearance, and is not sufficient to tint the paper. If the paper is to be blue laid, azure, or yellow wove, smalts is the colouring matter used. This is an indestructible blue, being cobalt glass reduced to extremely fine powder, and is used for the highest grades of papers, but many hand-made papers will be found to be coloured with ultramarine, which is a very good blue, but not quite so durable as smalts. Coloured papers require different additions, some in the form of powders or dry colours, others in chemical solutions, which by combination produce the desired colour in the pulp. When thoroughly mixed, the pulp is let down to the stuff chests and kept in constant motion by revolving paddles. The vat at which the paper vatman—stands is kept supplied with pulp, diluted to a regular consistency, kept in motion by an agitator, and a constant temperature is maintained. The mould used is a wooden frame, strengthened by ribs across its width, and a wire top of laid or woven wire. In the case of laid papers the wires are laid side by side, tying wires about an inch apart are superimposed, and fastened to the laid wires by very fine brass wire. These wires make an indelible impression upon all paper made upon the mould, and distinguish laid from wove papers, the latter being made upon a woven wire mould. Watermarks are the results of designs in reverse fastened to the mould, the design being formed with wire upon the mould, or else an electrotyped mark is soldered to the mould.

Watermarks may be simply small designs or lettering, or they may take the form of elaborate pictorial designs, but their purpose is to add distinction to the paper, and in some cases to prevent forgery of valuable notes or documents. Upon the mould is laid an open frame, known as the deckle, which serves to confine the pulp to the mould. For all papers two moulds are used in order to continue the cycle of operations uninterruptedly.

The vatman takes a mould, places the deckle upon it, dips the mould into the vat of diluted pulp, and lifts just the quantity of pulp necessary for the weight of paper being made. A slight shake is given to the mould, a small side shake and a greater shake backwards and forwards, something like the shake given to a type case, but less violent, the object being to cause the individual fibres to cross and felt together. The mould is kept perfectly level, or the sheets are thinner at one edge than at the others, the mould is pushed

along a support by the side of the vat, the deckle removed, and the operations of moulding repeated with the second mould.

The coucher who places the paper upon the felts ready for pressing, or couching, stands to the left of and facing the vatman. He takes the mould, stands it at an angle to drain, and places the mould face downwards upon a felt; the paper remains on the felt, and the mould is returned to the vatman. The felts are woollen cloths of close texture, resembling that of machine blankets, and are larger than the paper placed upon them.

Upon each sheet of paper a third worker places a felt, and the papermaking proceeds. When the pile of felts and paper is sufficiently high, it is transferred to a hydraulic press, and considerable pressure is applied in order to remove as much water as possible by squeezing, and, more important, to couch or press the fibres together and to close the sheets. The pile is removed, the felts taken out, the pile of paper given further pressing, and for some papers the paper is turned, rebuilt, and pressed again, to improve the closeness of the sheets. The paper is then taken to the drying loft, hung on ropes of cow hair, which material possesses the virtue of making no marks or stains upon the tender paper. Loft-drying is carried on at an even temperature, in order to permit of even shrinkage of the sheets. At this stage the paper, which is unsized, is known as waterleaf, and unless it is to be used in the unsized state, requires further treatment, as described in the next chapter, before being ready for use.

Mould-made papers are made by machine as far as making the sheets is concerned, other operations being carried out as for hand-made papers. The moulding or forming of the sheet is carried out in different ways on different machines, but the construction of the machines being kept secret by their users, it is not possible to give a description here.

Machine-made Papers

CHAPTER IV

PAPERMAKING BY MACHINE

The Fourdrinier machine bears the same relation to the hand mould that the rotary press does to the hand press. Instead of making paper sheet by sheet, it makes it in a continuous web, on an endless band of woven wire. The machine in a much simpler form was invented by a Frenchman, Nicholas Robert, the first machine being made in 1799, and so rapidly did the machine find favour that in fifty years over 150 papermaking machines were at work.

Papermaking by hand involves the processes of transferring a certain and regular quantity of pulp from the vat to the mould, shaking the mould to felt the fibres and to remove the water, couching the paper and drying the waterleaf. Machine-made paper follows the same processes exactly, everything being done by the one machine, including sizing. Viewing the papermaking machine, it appears to be a collection of machines carrying out the separate functions in proper sequence. The different parts of the machine can be controlled and driven at different speeds for special reasons. Thus a definite and regular quantity of pulp is taken, shaken, the water removed, the soft paper couched, pressed, dried, and a finish given to the surface of the paper, all in the compass of the one machine.

The pulp as left at the end of Chapter II. was merely beaten fibre, and if an unsized paper

required the pulp would be let down to the stuff-chest; but usually other things are added before the pulp is ready for the machine. Filling or loading, colouring matter and sizing material, are mixed with the pulp, thoroughly incorporated, and then the engine is emptied. Paper can be made without filling or loading; in fact all-rag papers seldom contain mineral matter, and many excellent papers are made from other fibres without loading. The purposes of loading are to fill the spaces between the fibres, to give opacity to papers, such as those made of sulphite wood pulp, which would otherwise be very transparent, and to enable the paper to take a higher finish than would be possible in a paper without loading: a smoother and more absorbent, even if a little weaker, sheet, resulting. In a blotting paper mineral matter is an adulteration; in writing papers 5 per cent, is sufficient for improvement of surface; in printings 10 to 16 per cent, is as much as is permissible. In an imitation art paper as much as 25 per cent, may be added, and yet a serviceable paper result; but of course the tenderness of imitation art paper will be present.

China clay is the usual material used for filling or loading. It is mixed with water, and strained before filling into the beating engine, and the colour is added, either to produce a coloured paper, or to correct the tendency to greyness in the finished paper. In the latter case, a little blue and perhaps a little red is added, while in the former case the colour may be added, or formed in situ by the mixture of different chemicals in the beating engine. Dry colours, whether pigment as ultramarine or aniline colours, are mixed with water (dry patches being difficult to deal with in the pulp), and then added to the pulp in the engine; when the colours are thoroughly mixed, alum is put in. Alum serves to mordant or fix the colour, and also serves to precipitate the resin size which is next added.

There are various prepared sizes on the market to take the place of the size prepared by the papermaker from resin and a solution of soda. The resin is melted and added to the soda solution, and boiled until the solution is complete. The size solution is added to the pulp in the beating engine, and thus we get a clue to the meaning of E.S., or engine-sized paper.

The pulp now consists of innumerable fibres, to which and in which are fixed small particles of china clay, colouring matter, and resin. In many writing papers a small amount of starch paste is added, and that also adheres to the tiny fibres. The engine is emptied by gravity into the stuff-chest, where the revolving arms keep the fibres in the mixture from precipitation. Then there is a short journey to the machine, during which the pulp undergoes great tribulation, first being diluted with a large quantity of water, then passing over sand traps which intercept grit, metallic fragments, and such matter that is heavier than the pulp and so tends to sink, and then through strainers, which retain foreign matter, unbeaten particles, and knots of fibre. The flow of pulp is governed by a system of valves, which can be quickly manipulated to alter the substance of the resulting paper.

The wet end of the machine consists of an endless band of woven wire, some 40 to 80 meshes to the inch, from 48 to 205 inches wide, and a total length of 40 feet or more. The length of wire in use at one time as a paper mould is less than half its total length. This woven wire corresponds to the mould of the vatman in hand-making. Deckle straps, the substitutes for the vatman's deckle, are thick endless rubber bands, square in section, which rest on the wire cloth, and, following the travel of the wire, return over pulleys, serving the same purpose as the deckle, namely, to confine the pulp to the wire surface. The wire cloth is supported by a number of rollers—tube rolls—which keep the wire from oscillating, and assist the passage of the water through the wire. The end of the wire nearest the stuff-chest is kept shaking backwards and forwards to cause the